[mrg666]

This is the third time i fixed my P0172 CEL. Wanted to list the fixes here for the others who might ask for a fix.

Symptoms were all same
- Engine service and traction control off light come up, OBDII reports P0172 (system too rich)
- MAF reading during warm idle is above 3.5
- Rough idle, reduced power, and an overall noisy engine. Especially after the catback, exhaust sound was drony and much louder than normal. Engine is hesitant to rev up.

Fixes
1- The first time fix required just cleaning and reseating the MAF sensor
2- Second time months later was much harder since I had to chase down leaking vacuum lines. The two vacuum lines under the intake manifold connecting to the solenoid, their both ends (i.e. four ends of two lines) needed to be clamped. All of them were completely loose.
3- I fixed this CEL third time yesterday for a completely different reason. Oil catch can was completely full and overflowing. That is PCV not crankcase; crankcase never collects any oil. Cleaning and resetting the CEL fixed the problem immediately.

Hope this helps someone ...

Edit: I have not seen any other CEL and hope this is the last time. But all of the causes were my error as the person servicing my own car.